Network Working Group M. Bjorklund
Internet-Draft Tail-f Systems
Updates: 7950 (if approved) J. Schoenwaelder
Intended status: Standards Track Jacobs University
Expires: May 3, 2018 P. Shafer
K. Watsen
Juniper Networks
R. Wilton
Cisco Systems
October 30, 2017
Network Management Datastore Architecturedraft-ietf-netmod-revised-datastores-06
Abstract
Datastores are a fundamental concept binding the data models written
in the YANG data modeling language to network management protocols
such as NETCONF and RESTCONF. This document defines an architectural
framework for datastores based on the experience gained with the
initial simpler model, addressing requirements that were not well
supported in the initial model.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 3, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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The duplication of definitions and the ad-hoc separation of
operational state data from configuration data leads to a number of
problems. Having configuration and operational state data in
separate branches in the data model is operationally complicated and
impacts the readability of module definitions. Furthermore, the
relationship between the branches is not machine readable and filter
expressions operating on configuration and on related operational
state are different.
With the revised architectural model of datastores defined in this
document, the data objects are defined only once in the YANG schema
but independent instantiations can appear in two different
datastores, one for configured values and one for operational state
values. This provides a more elegant and simpler solution to the
problem.
The revised architectural model of datastores supports additional
datastores for systems that support more advanced processing chains
converting configuration to operational state. For example, some
systems support configuration that is not currently used (so called
inactive configuration) or they support configuration templates that
are used to expand configuration data via a common template.
3. Terminology
This document defines the following terminology. Some of the terms
are revised definitions of terms originally defined in [RFC6241] and
[RFC7950] (see also section Section 4). The revised definitions are
semantically equivalent with the definitions found in [RFC6241] and
[RFC7950]. It is expected that the revised definitions provided in
this section will replace the definitions in [RFC6241] and [RFC7950]
when these documents are revised.
o datastore: A conceptual place to store and access information. A
datastore might be implemented, for example, using files, a
database, flash memory locations, or combinations thereof. A
datastore maps to an instantiated YANG data tree.
o schema node: A node in the schema tree. The formal definition is
in RFC 7950.
o datastore schema: The combined set of schema nodes for all modules
supported by a particular datastore, taking into consideration any
deviations and enabled features for that datastore.
o configuration: Data that is required to get a device from its
initial default state into a desired operational state. This data
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is modeled in YANG using "config true" nodes. Configuration can
originate from different sources.
o configuration datastore: A datastore holding configuration.
o running configuration datastore: A configuration datastore holding
the current configuration of the device. It may include
configuration that requires further transformations before it can
be applied. This datastore is referred to as "<running>".
o candidate configuration datastore: A configuration datastore that
can be manipulated without impacting the device's running
configuration datastore and that can be committed to the running
configuration datastore. This datastore is referred to as
"<candidate>".
o startup configuration datastore: A configuration datastore holding
the configuration loaded by the device into the running
configuration datastore when it boots. This datastore is referred
to as "<startup>".
o intended configuration: Configuration that is intended to be used
by the device. It represents the configuration after all
configuration transformations to <running> have been performed and
is the configuration that the system attempts to apply.
o intended configuration datastore: A configuration datastore
holding the complete intended configuration of the device. This
datastore is referred to as "<intended>".
o configuration transformation: The addition, modification or
removal of configuration between the <running> and <intended>
datastores. Examples of configuration transformations include the
removal of inactive configuration and the configuration produced
through the expansion of templates.
o conventional configuration datastore: One of the following set of
configuration datastores: <running>, <startup>, <candidate>, and
<intended>. These datastores share a common datastore schema, and
protocol operations allow copying data between these datastores.
The term "conventional" is chosen as a generic umbrella term for
these datastores.
o conventional configuration: Configuration that is stored in any of
the conventional configuration datastores.
o dynamic configuration datastore: A configuration datastore holding
configuration obtained dynamically during the operation of a
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device through interaction with other systems, rather than through
one of the conventional configuration datastores.
o dynamic configuration: Configuration obtained via a dynamic
configuration datastore.
o learned configuration: Configuration that has been learned via
protocol interactions with other systems and that is neither
conventional nor dynamic configuration.
o system configuration: Configuration that is supplied by the device
itself.
o default configuration: Configuration that is not explicitly
provided but for which a value defined in the data model is used.
o applied configuration: Configuration that is actively in use by a
device. Applied configuration originates from conventional,
dynamic, learned, system and default configuration.
o system state: The additional data on a system that is not
configuration, such as read-only status information and collected
statistics. System state is transient and modified by
interactions with internal components or other systems. System
state is modeled in YANG using "config false" nodes.
o operational state: The combination of applied configuration and
system state.
o operational state datastore: A datastore holding the complete
operational state of the device. This datastore is referred to as
"<operational>".
o origin: A metadata annotation indicating the origin of a data
item.
o remnant configuration: Configuration that remains part of the
applied configuration for a period of time after it has been
removed from the intended configuration or dynamic configuration.
The time period may be minimal, or may last until all resources
used by the newly-deleted configuration (e.g., network
connections, memory allocations, file handles) have been
deallocated.
The following additional terms are not datastore specific but
commonly used and thus defined here as well:
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o client: An entity that can access YANG-defined data on a server,
over some network management protocol.
o server: An entity that provides access to YANG-defined data to a
client, over some network management protocol.
o notification: A server-initiated message indicating that a certain
event has been recognized by the server.
o remote procedure call: An operation that can be invoked by a
client on a server.
4. Background
NETCONF [RFC6241] provides the following definitions:
o datastore: A conceptual place to store and access information. A
datastore might be implemented, for example, using files, a
database, flash memory locations, or combinations thereof.
o configuration datastore: The datastore holding the complete set of
configuration that is required to get a device from its initial
default state into a desired operational state.
YANG 1.1 [RFC7950] provides the following refinements when NETCONF is
used with YANG (which is the usual case but note that NETCONF was
defined before YANG existed):
o datastore: When modeled with YANG, a datastore is realized as an
instantiated data tree.
o configuration datastore: When modeled with YANG, a configuration
datastore is realized as an instantiated data tree with
configuration.
[RFC6244] defined operational state data as follows:
o Operational state data is a set of data that has been obtained by
the system at runtime and influences the system's behavior similar
to configuration data. In contrast to configuration data,
operational state is transient and modified by interactions with
internal components or other systems via specialized protocols.
Section 4.3.3 of [RFC6244] discusses operational state and among
other things mentions the option to consider operational state as
being stored in another datastore. Section 4.4 of this document then
concludes that at the time of the writing, modeling state as distinct
leafs and distinct branches is the recommended approach.
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Implementation experience and requests from operators
[I-D.ietf-netmod-opstate-reqs], [I-D.openconfig-netmod-opstate]
indicate that the datastore model initially designed for NETCONF and
refined by YANG needs to be extended. In particular, the notion of
intended configuration and applied configuration has developed.
4.1. Original Model of Datastores
The following drawing shows the original model of datastores as it is
currently used by NETCONF [RFC6241]:
+-------------+ +-----------+
| <candidate> | | <startup> |
| (ct, rw) |<---+ +--->| (ct, rw) |
+-------------+ | | +-----------+
| | | |
| +-----------+ |
+-------->| <running> |<--------+
| (ct, rw) |
+-----------+
|
v
operational state <--- control plane
(cf, ro)
ct = config true; cf = config false
rw = read-write; ro = read-only
boxes denote datastores
Note that this diagram simplifies the model: read-only (ro) and read-
write (rw) is to be understood at a conceptual level. In NETCONF,
for example, support for <candidate> and <startup> is optional and
<running> does not have to be writable. Furthermore, <startup> can
only be modified by copying <running> to <startup> in the
standardized NETCONF datastore editing model. The RESTCONF protocol
does not expose these differences and instead provides only a
writable unified datastore, which hides whether edits are done
through <candidate> or by directly modifying <running> or via some
other implementation specific mechanism. RESTCONF also hides how
configuration is made persistent. Note that implementations may also
have additional datastores that can propagate changes to <running>.
NETCONF explicitly mentions so called named datastores.
Some observations:
o Operational state has not been defined as a datastore although
there were proposals in the past to introduce an operational state
datastore.
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o The NETCONF <get> operation returns the contents of <running>
together with the operational state. It is therefore necessary
that "config false" data is in a different branch than the "config
true" data if the operational state can have a different lifetime
compared to configuration or if configuration is not immediately
or successfully applied.
o Several implementations have proprietary mechanisms that allow
clients to store inactive data in <running>. Inactive data is
conceptually removed before validation.
o Some implementations have proprietary mechanisms that allow
clients to define configuration templates in <running>. These
templates are expanded automatically by the system, and the
resulting configuration is applied internally.
o Some operators have reported that it is essential for them to be
able to retrieve the configuration that has actually been
successfully applied, which may be a subset or a superset of the
<running> configuration.
5. Architectural Model of Datastores
Below is a new conceptual model of datastores extending the original
model in order to reflect the experience gained with the original
model.
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o <startup>
o <intended>
Other conventional configuration datastores may be defined in future
documents.
The flow of data between these datastores is depicted in Section 5.
The specific protocols may define explicit operations to copy between
these datastores, e.g., NETCONF defines the <copy-config> operation.
5.1.1. The Startup Configuration Datastore (<startup>)
The startup configuration datastore (<startup>) is a configuration
datastore holding the configuration loaded by the device when it
boots. <startup> is only present on devices that separate the
startup configuration from the running configuration datastore.
The startup configuration datastore may not be supported by all
protocols or implementations.
On devices that support non-volatile storage, the contents of
<startup> will typically persist across reboots via that storage. At
boot time, the device loads the saved startup configuration into
<running>. To save a new startup configuration, data is copied to
<startup>, either via implicit or explicit protocol operations.
5.1.2. The Candidate Configuration Datastore (<candidate>)
The candidate configuration datastore (<candidate>) is a
configuration datastore that can be manipulated without impacting the
device's current configuration and that can be committed to
<running>.
The candidate configuration datastore may not be supported by all
protocols or implementations.
<candidate> does not typically persist across reboots, even in the
presence of non-volatile storage. If <candidate> is stored using
non-volatile storage, it is reset at boot time to the contents of
<running>.
5.1.3. The Running Configuration Datastore (<running>)
The running configuration datastore (<running>) is a configuration
datastore that holds the complete current configuration on the
device. It MAY include configuration that requires further
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transformation before it can be applied, e.g., inactive
configuration, or template-mechanism-oriented configuration that
needs further expansion. However, <running> MUST always be a valid
configuration data tree, as defined in Section 8.1 of [RFC7950].
<running> MUST be supported if the device can be configured via
conventional configuration datastores.
If a device does not have a distinct <startup> and non-volatile
storage is available, the device will typically use that non-volatile
storage to allow <running> to persist across reboots.
5.1.4. The Intended Configuration Datastore (<intended>)
The intended configuration datastore (<intended>) is a read-only
configuration datastore. It represents the configuration after all
configuration transformations to <running> are performed (e.g.,
template expansion, removal of inactive configuration), and is the
configuration that the system attempts to apply.
<intended> is tightly coupled to <running>. Whenever data is written
to <running>, then <intended> MUST also be immediately updated by
performing all necessary configuration transformations to the
contents of <running> and then <intended> is validated.
<intended> MAY also be updated independently of <running> if the
effect of a configuration transformation changes, but <intended> MUST
always be a valid configuration data tree, as defined in Section 8.1
of [RFC7950].
For simple implementations, <running> and <intended> are identical.
The contents of <intended> are also related to the "config true"
subset of <operational>, and hence a client can determine to what
extent the intended configuration is currently in use by checking
whether the contents of <intended> also appear in <operational>.
<intended> does not persist across reboots; its relationship with
<running> makes that unnecessary.
Currently there are no standard mechanisms defined that affect
<intended> so that it would have different content than <running>,
but this architecture allows for such mechanisms to be defined.
One example of such a mechanism is support for marking nodes as
inactive in <running>. Inactive nodes are not copied to <intended>.
A second example is support for templates, which can perform
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transformations on the configuration from <running> to the
configuration written to <intended>.
5.2. Dynamic Configuration Datastores
The model recognizes the need for dynamic configuration datastores
that are, by definition, not part of the persistent configuration of
a device. In some contexts, these have been termed ephemeral
datastores since the information is ephemeral, i.e., lost upon
reboot. The dynamic configuration datastores interact with the rest
of the system through <operational>.
5.3. The Operational State Datastore (<operational>)
The operational state datastore (<operational>) is a read-only
datastore that consists of all "config true" and "config false" nodes
defined in the datastore's schema. In the original NETCONF model the
operational state only had "config false" nodes. The reason for
incorporating "config true" nodes here is to be able to expose all
operational settings without having to replicate definitions in the
data models.
<operational> contains system state and all configuration actually
used by the system. This includes all applied configuration from
<intended>, learned configuration, system-provided configuration, and
default values defined by any supported data models. In addition,
<operational> also contains applied configuration from dynamic
configuration datastores.
The datastore schema for <operational> MUST be a superset of the
combined datastore schema used in all configuration datastores except
that YANG nodes supported in a configuration datastore MAY be omitted
from <operational> if a server is not able to accurately report them.
Requests to retrieve nodes from <operational> always return the value
in use if the node exists, regardless of any default value specified
in the YANG module. If no value is returned for a given node, then
this implies that the node is not used by the device.
The interpretation of what constitutes as being "in use" by the
system is dependent on both the schema definition and the device
implementation. Generally, functionality that is enabled and
operational on the system would be considered as being "in use".
Conversely, functionality that is neither enabled nor operational on
the system is considered as not being "in use", and hence SHOULD be
omitted from <operational>.
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<operational> SHOULD conform to any constraints specified in the data
model, but given the principal aim of returning "in use" values, it
is possible that constraints MAY be violated under some
circumstances, e.g., an abnormal value is "in use", the structure of
a list is being modified, or due to remnant configuration (see
Section 5.3.1). Note, that deviations SHOULD be used when it is
known in advance that a device does not fully conform to the
<operational> schema.
Only semantic constraints MAY be violated, these are the YANG "when",
"must", "mandatory", "unique", "min-elements", and "max-elements"
statements; and the uniqueness of key values.
Syntactic constraints MUST NOT be violated, including hierarchical
organization, identifiers, and type-based constraints. If a node in
<operational> does not meet the syntactic constraints then it MUST
NOT be returned, and some other mechanism should be used to flag the
error.
<operational> does not persist across reboots.
5.3.1. Remnant Configuration
Changes to configuration may take time to percolate through to
<operational>. During this period, <operational> may contain nodes
for both the previous and current configuration, as closely as
possible tracking the current operation of the device. Such remnant
configuration from the previous configuration persists until the
system has released resources used by the newly-deleted configuration
(e.g., network connections, memory allocations, file handles).
Remnant configuration is a common example of where the semantic
constraints defined in the data model cannot be relied upon for
<operational>, since the system may have remnant configuration whose
constraints were valid with the previous configuration and that are
not valid with the current configuration. Since constraints on
"config false" nodes may refer to "config true" nodes, remnant
configuration may force the violation of those constraints.
5.3.2. Missing Resources
Configuration in <intended> can refer to resources that are not
available or otherwise not physically present. In these situations,
these parts of <intended> are not applied. The data appears in
<intended> but does not appear in <operational>.
A typical example is an interface configuration that refers to an
interface that is not currently present. In such a situation, the
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interface configuration remains in <intended> but the interface
configuration will not appear in <operational>.
Note that configuration validity cannot depend on the current state
of such resources, since that would imply that removing a resource
might render the configuration invalid. This is unacceptable,
especially given that rebooting such a device would cause it to
restart with an invalid configuration. Instead we allow
configuration for missing resources to exist in <running> and
<intended>, but it will not appear in <operational>.
5.3.3. System-controlled Resources
Sometimes resources are controlled by the device and the
corresponding system controlled data appears in (and disappears from)
<operational> dynamically. If a system controlled resource has
matching configuration in <intended> when it appears, the system will
try to apply the configuration, which causes the configuration to
appear in <operational> eventually (if application of the
configuration was successful).
5.3.4. Origin Metadata Annotation
As configuration flows into <operational>, it is conceptually marked
with a metadata annotation ([RFC7952]) that indicates its origin.
The origin applies to all configuration nodes except non-presence
containers. The "origin" metadata annotation is defined in
Section 7. The values are YANG identities. The following identities
are defined:
o origin: abstract base identity from which the other origin
identities are derived.
o intended: represents configuration provided by <intended>.
o dynamic: represents configuration provided by a dynamic
configuration datastore.
o system: represents configuration provided by the system itself.
Examples of system configuration include applied configuration for
an always existing loopback interface, or interface configuration
that is auto-created due to the hardware currently present in the
device.
o learned: represents configuration that has been learned via
protocol interactions with other systems, including protocols such
as link-layer negotiations, routing protocols, DHCP, etc.
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o default: represents configuration using a default value specified
in the data model, using either values in the "default" statement
or any values described in the "description" statement. The
default origin is only used when the configuration has not been
provided by any other source.
o unknown: represents configuration for which the system cannot
identify the origin.
These identities can be further refined, e.g., there could be
separate identities for particular types or instances of dynamic
configuration datastores derived from "dynamic".
For all configuration data nodes in <operational>, the device SHOULD
report the origin that most accurately reflects the source of the
configuration that is in use by the system.
In cases where it could be ambiguous as to which origin should be
used, i.e. where the same data node value has originated from
multiple sources, then the description statement in the YANG module
SHOULD be used as guidance for choosing the appropriate origin. For
example:
If for a particular configuration node, the associated YANG
description statement indicates that a protocol negotiated value
overrides any configured value, then the origin would be reported as
"learned", even when a learned value is the same as the configured
value.
Conversely, if for a particular configuration node, the associated
YANG description statement indicates that a protocol negotiated value
does not override an explicitly configured value, then the origin
would be reported as "intended" even when a learned value is the same
as the configured value.
In the case that a device cannot provide an accurate origin for a
particular configuration data node then it SHOULD use the origin
"unknown".
6. Implications on YANG6.1. XPath Context
This section updates section 6.4.1 of RFC 7950.
If a server implements the architecture defined in this document, the
accessible trees for some XPath contexts are refined as follows:
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o If the XPath expression is defined in a substatement to a data
node that represents system state, the accessible tree is all
operational state in the server. The root node has all top-level
data nodes in all modules as children.
o If the XPath expression is defined in a substatement to a
"notification" statement, the accessible tree is the notification
instance and all operational state in the server. If the
notification is defined on the top level in a module, then the
root node has the node representing the notification being defined
and all top-level data nodes in all modules as children.
Otherwise, the root node has all top-level data nodes in all
modules as children.
o If the XPath expression is defined in a substatement to an "input"
statement in an "rpc" or "action" statement, the accessible tree
is the RPC or action operation instance and all operational state
in the server. The root node has top-level data nodes in all
modules as children. Additionally, for an RPC, the root node also
has the node representing the RPC operation being defined as a
child. The node representing the operation being defined has the
operation's input parameters as children.
o If the XPath expression is defined in a substatement to an
"output" statement in an "rpc" or "action" statement, the
accessible tree is the RPC or action operation instance and all
operational state in the server. The root node has top-level data
nodes in all modules as children. Additionally, for an RPC, the
root node also has the node representing the RPC operation being
defined as a child. The node representing the operation being
defined has the operation's output parameters as children.
7. YANG Modules
<CODE BEGINS> file "ietf-datastores@2017-08-17.yang"
module ietf-datastores {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-datastores";
prefix ds;
organization
"IETF Network Modeling (NETMOD) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
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description
"Denotes configuration originated by the system itself.
Examples of system configuration include applied configuration
for an always existing loopback interface, or interface
configuration that is auto-created due to the hardware
currently present in the device.";
}
identity learned {
base origin;
description
"Denotes configuration learned from protocol interactions with
other devices, instead of via either the intended
configuration datastore or any dynamic configuration
datastore.
Examples of protocols that provide learned configuration
include link-layer negotiations, routing protocols, and
DHCP.";
}
identity default {
base origin;
description
"Denotes configuration that does not have an configured or
learned value, but has a default value in use. Covers both
values defined in a 'default' statement, and values defined
via an explanation in a 'description' statement.";
}
identity unknown {
base origin;
description
"Denotes configuration for which the system cannot identify the
origin.";
}
/*
* Type definitions
*/
typedef origin-ref {
type identityref {
base origin;
}
description
"An origin identity reference.";
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}
/*
* Metadata annotations
*/
md:annotation origin {
type origin-ref;
description
"The 'origin' annotation can be present on any configuration
data node in the operational datastore. It specifies from
where the node originated. If not specified for a given
configuration data node then the origin is the same as the
origin of its parent node in the data tree. The origin for
any top level configuration data nodes must be specified.";
}
}
<CODE ENDS>
8. IANA Considerations8.1. Updates to the IETF XML Registry
This document registers two URIs in the IETF XML registry [RFC3688].
Following the format in [RFC3688], the following registrations are
requested:
URI: urn:ietf:params:xml:ns:yang:ietf-datastores
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-origin
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
8.2. Updates to the YANG Module Names Registry
This document registers two YANG modules in the YANG Module Names
registry [RFC6020]. Following the format in [RFC6020], the the
following registrations are requested:
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connected). Each datastore's definition should address the points
specified in the sections below.
A.1. Define which YANG modules can be used in the datastore
Not all YANG modules may be used in all datastores. Some datastores
may constrain which data models can be used in them. If it is
desirable that a subset of all modules can be targeted to the
datastore, then the documentation defining the datastore must
indicate this.
A.2. Define which subset of YANG-modeled data applies
By default, the data in a datastore is modeled by all YANG statements
in the available YANG modules. However, it is possible to specify
criteria that YANG statements must satisfy in order to be present in
a datastore. For instance, maybe only "config true" nodes, or
"config false" nodes that also have a specific YANG extension, are
present in the datastore.
A.3. Define how data is actualized
The new datastore must specify how it interacts with other
datastores.
For example, the diagram in Section 5 depicts dynamic configuration
datastores feeding into <operational>. How this interaction occurs
has to be defined by the particular dynamic configuration datastores.
In some cases, it may occur implicitly, as soon as the data is put
into the dynamic configuration datastore while, in other cases, an
explicit action (e.g., an RPC) may be required to trigger the
application of the datastore's data.
A.4. Define which protocols can be used
By default, it is assumed that both the NETCONF and RESTCONF
protocols can be used to interact with a datastore. However, it may
be that only a specific protocol can be used (e.g., ForCES) or that a
subset of all protocol operations or capabilities are available
(e.g., no locking or no XPath-based filtering).
A.5. Define YANG identities for the datastore
The datastore must be defined with a YANG identity that uses the
"ds:datastore" identity, or one of its derived identities, as its
base. This identity is necessary so that the datastore can be
referenced in protocol operations (e.g., <get-data>).
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The datastore may also be defined with an identity that uses the
"or:origin" identity or one its derived identities as its base. This
identity is needed if the datastore interacts with <operational> so
that data originating from the datastore can be identified as such
via the "origin" metadata attribute defined in Section 7.
An example of these guidelines in use is provided in Appendix B.
Appendix B. Ephemeral Dynamic Configuration Datastore Example
The section defines documentation for an example dynamic
configuration datastore using the guidelines provided in Appendix A.
While this example is very terse, it is expected to be that a
standalone RFC would be needed when fully expanded.
This example defines a dynamic configuration datastore called
"ephemeral", which is loosely modeled after the work done in the I2RS
working group.
+--------------+---------------------------------------------------+
| Name | Value |
+--------------+---------------------------------------------------+
| Name | ephemeral |
| YANG modules | all (default) |
| YANG nodes | all "config true" data nodes |
| How applied | changes automatically propagated to <operational> |
| Protocols | NC/RC (default) |
| YANG Module | (see below) |
+--------------+---------------------------------------------------+
The example "ephemeral" datastore properties
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The operator has configured the host name and two interfaces, so the
contents of <intended> are:
<system xmlns="urn:example:system">
<hostname>foo</hostname>
<interface>
<name>eth0</name>
<auto-negotiation>
<speed>1000</speed>
</auto-negotiation>
<address>
<ip>2001:db8::10</ip>
<prefix-length>64</prefix-length>
</address>
</interface>
<interface>
<name>eth1</name>
<address>
<ip>2001:db8::20</ip>
<prefix-length>64</prefix-length>
</address>
</interface>
</system>
The system has detected that the hardware for one of the configured
interfaces ("eth1") is not yet present, so the configuration for that
interface is not applied. Further, the system has received a host
name and an additional IP address for "eth0" over DHCP. In addition
to a default value, a loopback interface is automatically added by
the system, and the result of the "speed" auto-negotiation. All of
this is reflected in <operational>. Note how the origin metadata
attribute for several "config true" data nodes is inherited from
their parent data nodes.
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repetition of containment and naming nodes. This makes the model
simpler and more readable.
C.2.1. Datastores
Each datastore represents differing views of these nodes. <running>
will hold the configuration provided by the operator, for example a
single BGP peer. <intended> will conceptually hold the data as
validated, after the removal of data not intended for validation and
after any local template mechanisms are performed. <operational>
will show data from <intended> as well as any "config false" nodes.
C.2.2. Adding a Peer
If the user configures a single BGP peer, then that peer will be
visible in both <running> and <intended>. It may also appear in
<candidate>, if the server supports the candidate configuration
datastore. Retrieving the peer will return only the user-specified
values.
No time delay should exist between the appearance of the peer in
<running> and <intended>.
In this scenario, we've added the following to <running>:
<bgp>
<local-as>64501</local-as>
<peer-as>64502</peer-as>
<peer>
<name>10.1.2.3</name>
</peer>
</bgp>
C.2.2.1. <operational>
The operational datastore will contain the fully expanded peer data,
including "config false" nodes. In our example, this means the
"state" node will appear.
In addition, <operational> will contain the "currently in use" values
for all nodes. This means that local-as and peer-as will be
populated even if they are not given values in <intended>. The value
of bgp/local-as will be used if bgp/peer/local-as is not provided;
bgp/peer-as and bgp/peer/peer-as will have the same relationship. In
the operational view, this means that every peer will have values for
their local-as and peer-as, even if those values are not explicitly
configured but are provided by bgp/local-as and bgp/peer-as.
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Each BGP peer has a TCP connection associated with it, using the
values of local-port and remote-port from <intended>. If those
values are not supplied, the system will select values. When the
connection is established, <operational> will contain the current
values for the local-port and remote-port nodes regardless of the
origin. If the system has chosen the values, the "origin" attribute
will be set to "system". Before the connection is established, one
or both of the nodes may not appear, since the system may not yet
have their values.
<bgp or:origin="or:intended">
<local-as>64501</local-as>
<peer-as>64502</peer-as>
<peer>
<name>10.1.2.3</name>
<local-as or:origin="or:default">64501</local-as>
<peer-as or:origin="or:default">64502</peer-as>
<local-port or:origin="or:system">60794</local-port>
<remote-port or:origin="or:default">179</remote-port>
<state>established</state>
</peer>
</bgp>
C.2.3. Removing a Peer
Changes to configuration may take time to percolate through the
various software components involved. During this period, it is
imperative to continue to give an accurate view of the working of the
device. <operational> will contain nodes for both the previous and
current configuration, as closely as possible tracking the current
operation of the device.
Consider the scenario where a client removes a BGP peer. When a peer
is removed, the operational state will continue to reflect the
existence of that peer until the peer's resources are released,
including closing the peer's connection. During this period, the
current data values will continue to be visible in <operational>,
with the "origin" attribute set to indicate the origin of the
original data.
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<bgp or:origin="or:intended">
<local-as>64501</local-as>
<peer-as>64502</peer-as>
<peer>
<name>10.1.2.3</name>
<local-as or:origin="or:default">64501</local-as>
<peer-as or:origin="or:default">64502</peer-as>
<local-port or:origin="or:system">60794</local-port>
<remote-port or:origin="or:default">179</remote-port>
<state>closing</state>
</peer>
</bgp>
Once resources are released and the connection is closed, the peer's
data is removed from <operational>.
C.3. Interface Example
In this section, we will use this simple interface data model:
container interfaces {
list interface {
key name;
leaf name {
type string;
}
leaf description {
type string;
}
leaf mtu {
type uint16;
}
leaf-list ip-address {
type inet:ip-address;
}
}
}
C.3.1. Pre-provisioned Interfaces
One common issue in networking devices is the support of Field
Replaceable Units (FRUs) that can be inserted and removed from the
device without requiring a reboot or interfering with normal
operation. These FRUs are typically interface cards, and the devices
support pre-provisioning of these interfaces.
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If a client creates an interface "et-0/0/0" but the interface does
not physically exist at this point, then <intended> might contain the
following:
<interfaces>
<interface>
<name>et-0/0/0</name>
<description>Test interface</description>
</interface>
</interfaces>
Since the interface does not exist, this data does not appear in
<operational>.
When a FRU containing this interface is inserted, the system will
detect it and process the associated configuration. <operational>
will contain the data from <intended>, as well as nodes added by the
system, such as the current value of the interface's MTU.
<interfaces or:origin="or:intended">
<interface>
<name>et-0/0/0</name>
<description>Test interface</description>
<mtu or:origin="or:system">1500</mtu>
</interface>
</interfaces>
If the FRU is removed, the interface data is removed from
<operational>.
C.3.2. System-provided Interface
Imagine if the system provides a loopback interface (named "lo0")
with a default ip-address of "127.0.0.1" and a default ip-address of
"::1". The system will only provide configuration for this interface
if there is no data for it in <intended>.
When no configuration for "lo0" appears in <intended>, then
<operational> will show the system-provided data:
<interfaces or:origin="or:intended">
<interface or:origin="or:system">
<name>lo0</name>
<ip-address>127.0.0.1</ip-address>
<ip-address>::1</ip-address>
</interface>
</interfaces>
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